He never showed remorse or regret for his actions, a court heard as he was jailed for a minimum 23-year life sentence.

Karen was killed as she walked home alone from a Glasgow nightclub on April 12.

Justice Lady Rae said it was "extraordinary" for Pacteau to claim that his efforts to dispose of the young woman's body in first a bath and then a barrel of caustic soda should not be an aggravating factor in deciding the length of his life sentence.

The judge also noted that, in one social services report, Pacteau never once used phrases like "sorry", "remorse" or "regret" when talking about Karen's brutal killing.

Pacteau remained silent throughout the 18-minute hearing.

"Your killing of this young woman, combined with the extraordinary lengths to which you went to cover it up, display the actions of a callous and calculating man," she said.

"You destroyed her young life and devastated her family."

Pacteau, who had never met Karen, offered her a lift home on Dumbarton Road at 1am on April 12 after she had left The Sanctuary nightclub in Glasgow's west end.

Minutes later he bludgeoned her to death with a heavy spanner in his Ford Focus car.

Pacteau took Karen's body back to his flat on Dorchester Avenue and attempted to destroy it by using caustic soda and drain unblocking fluid.

He later placed Karen's body in a 220 litre barrel full of chemicals and hid it at an isolated Glasgow hill farm at High Craigton.

However, thanks to skilled work by Police Scotland detectives, officers called to Pacteau's flat within 36 hours of Karen's disappearance.

They became immediately suspicious because of the overwhelming smell of bleach.

Karen's blood was later found in Pacteau's bedroom and bathroom. The murder weapon was found in the Forth & Clyde Canal where Pacteau had thrown it.

Glasgow High Court was told by Lord Advocate Frank Mulholland QC that there was no evidence of a sexual assault. Supported by two Police Scotland liaison officers, Karen's parents sat just four metres from the hulking figure of six foot four inch and 15 stone Pacteau in the South Court of Glasgow's High Court.

"Today's life sentence will not bring our beautiful Karen back," John Buckley said.

"Our little angel has been taken from us forever in the cruellest of ways. We mourn for her every day. It will, however, ensure that women are safe from harm from the truly evil coward who took our beautiful Karen's precious life.

"(We) hope that he is never released and spends every day in prison haunted by what he did."

The couple from Mourneabbey in north Cork said: "We all want to move on and try to piece our lives back together.

"We have three wonderful sons and we need to be there for each other as a family.

"Karen is at peace now and we know that she is in heaven looking down on us and helping us."

However, the couple said they were still traumatised by the thought of what their beloved daughter must have suffered at the hands of Pacteau.

John said: "Our hearts are broken at the thought of Karen's final moments on this world. The thought of her being alone, frightened and struggling for her life haunts us."